The present invention relates to a developing apparatus for use in image recording equipment which is implemented with an electrostatographic process and, more particularly, to a developing apparatus capable of preventing a dry developer in the form of a toner from leaking from a housing of the apparatus to the interior of the equipment.
A developing apparatus installed in an electrophotographic copier, facsimile machine, laser printer or similar image recording equipment which is implemented with an electrostatographic principle uses, in many cases, a dry two-component developer which is the mixture of a toner and a carrier. The developing apparatus includes a housing having an opening which is located to face the periphery of a photoconductive element or image carrier. A rotatable developing sleeve is disposed in the housing to face the photoconductive element through the opening. An agitating roller is also accommodated in the housing for agitating a toner being supplied and transporting it to the developing sleeve. Specifically, a dry two-component toner constituted by a toner and a carrier is deposited on the developing sleeve to form a magnet brush. The magnet brush is brought into contact with a latent image which is electrostatically formed on the photoconductive element by an electrostatographic process, whereby the toner is adhered to the latent image to turn it to a toner image. The developer remaining on the developing sleeve after the development is returned to the housing via a clearance existing between an edge portion of the housing and the developing sleeve while the the developing sleeve is rotated. A fresh toner is supplied to the returned developer which has lost a part of its toner due to the development. The fresh toner and the returned developer are agitated together by the agitating roller and fed again to the developing sleeve.
The housing is hermetically closed except for the opening through which the developing sleeve faces the photoconductive element, in order to prevent the leakage of the developer into the itnerior of the recording equipment. In this configuration, air flows into the housing while the developing sleeve is rotated. This, coupled with the rotation of the agitating roller, raises the pressure inside of the housing. A high pressure prevailing in the housing is apt to blow out a toner cloud through the clearance between the edge portion of the opening of the housing and the developing sleeve and further through the clearance between the edge of the opening and the photoconductive element, smearing the interior of the equipment.
A doctor blade is located upstream of a developing position where the developing sleeve and photoconductive element neighbor each other, and it is spaced apart from the developing sleeve by a small distance. A seal member is provided between an edge portion of the opening of the housing upstream of the developing position and the periphery of the photoconductive element. However, in a region downstream of the developing position, an adequate clearance has to be left between the developing sleeve and an edge portion of the opening of the housing in order to pass the developer or magnet brush deposited on the developing sleeve. An adequate clearance has to be provided between the downstream edge portion of the opening of the housing and the photoconductive element also, so that the toner image on the photoconductive element may pass without being disturbed. Hence, a toner cloud is blown out of the housing mainly through such two clearances downstream of the developing position.
Various approaches have heretofore been proposed to eliminate the blowoff of a toner cloud. For example, the housing may be provided with a vent and a filter which closes the vent, as disclosed in Japanese Laid-Open Patent Publication (Kokai) Nos. 56-46272, 60-3678 and 56-99604. The vent releases the internal pressure of the housing, while the filter prevents toner particles from flowing out through the vent. The implementation shown and described in the first-mentioned Laid-Open Patent Publication includes a vacuum pump or similar sucking device which is communicated to the vent by a piping. The implementation taught in the second-mentioned Laid-Open Patent Publication is such that air is forced from the clearance between the opening of the housing which faces the photoconductive element and the periphery of the photocoductive element to the interior of the housing by an air compressor and a piping. A drawback with these prior art schemes is that the vacuum pump, air compressor or similar extra device and its associated piping increases the cost of the apparatus. On the other hand, the third-mentioned Laid-Open Patent Publication causes the developing sleeve to rotate in the opposite direction to the photoconductive drum, so that a stream of air tending to such air through between the edge portion of the opening of the housing and the photoconductive element may be generated. However, when the rotating direction of the developing sleeve is not the same as that of the photoconductive element, there is a fear that a toner cloud is blown out of the housing.